The present invention is concerned with a process for the production of a metal or metal alloy powder wherein the particles of powder are of a flake-like nature.
Metal or metal alloy powders with particles of flake-like nature are widely used in coating materials, for example bodywork paints and lacquers, because of their pronounced metallic shine. Such a powder may be produced by mechanically crushing or grinding a ductile starting material, and the operation of forming the flakes may be effected simultaneously with the grinding or crushing operation, or as a separate mechanical process. A certain degree of ductility of the starting material is important in order for it to be capable of being worked into the form of flakes. Accordingly, the line of development followed in this connection was and is directed to improving the capability of the starting material, for being formed into flakes.
However, the ductile properties of the starting material used for producing the metal powder give rise to difficulty in regard to the operation of crushing or grinding the starting material, which is generally in the form of a grit, or granular material. Although it has been observed that a proportion of lead in the metal grit causes the starting material to be harder so that it can be crushed more easily, that has the disadvantageous result that the capacity for shaping of the powder particles is severely impaired and flakes can be formed only to a very limited degree. It is for that reason that in the past the problems involved in crushing the ductile starting material, and thus the higher costs involved in overcoming the particular problems encountered in the crushing or grinding process were accepted, because of the desirability of the starting materia being easier to shape into flakes. It was thought that it was not possible to solve the problem of enhancing the crushability of the starting material, while at the same time retaining the ductility of the starting material, by using suitable additives in the starting material.